Will the New Ebola Vaccine Help to End Outbreaks?

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Experts welcomed the news today that a recent trial of an Ebola
vaccine suggests the shot is highly effective at preventing the
disease, and said that the the vaccine may stem outbreaks in the
future even if not everyone is vaccinated.

The study shows that the new vaccine, known as VSV-ZEBOV, "may
help finally extinguish this [Ebola] outbreak," said Dr. Amesh
Adalja, an infectious-disease specialist and a senior associate
at the University of Pittsburgh Medical Center's Center for
Health Security.

In the study, researchers in Guinea vaccinated people who had
contact with people who were infected with
Ebola, as well as the contacts of those contacts — a
technique known as "ring vaccination" (referring to vaccinating
the ring of people surrounding a case).

The researchers measured the new vaccine's effectiveness by
comparing two groups of people who were all in such rings of
contact — one group included about 2,000 people who were
vaccinated immediately after a person with Ebola was diagnosed,
whereas the comparison group included 1,500 people who were
vaccinated 21 days after a person with Ebola was identified (the
so-called "delayed vaccine" group). The study was conducted
between April and July of this year.

No new cases of Ebola were found 10 or more days after
vaccination in the immediate vaccination group, whereas 16 people
developed Ebola in the delayed vaccination group. This shows that
for the people who received the vaccination immediately, the
vaccine was 100 percent effective, according to the study,
published today (July 31) in the journal The Lancet. [ 10
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"The study is really great news," Adalja said. "There was such a
dramatic difference," between the immediate and the delayed
vaccination group, said Adalja, who also noted that it's rare for
a study to find a vaccine has a 100 percent protection rate.

The new findings are part of a preliminary analysis of the
vaccine trial. If the results are confirmed by future research,
it could mean that ring vaccination — the same strategy used
decades ago to eradicate
smallpox — will be used in future Ebola outbreaks, Adalja
said.

That's important because "you don't have to have the entire
population vaccinated, you can just prioritize the contacts of
the individuals infected," Adalja said. "It makes it a much
easier task to stop an outbreak," he told Live Science. "It's
exactly how they got smallpox to be beaten off the planet."

Dr. Jesse Goodman, a professor of medicine at Georgetown
University Medical Center in Washington D.C., said although more
information from the study is needed, "this is very good news
today and suggests that the [new vaccine] is effective and
can be an important tool in outbreak control, including through
ring vaccination."

However, some questions still remain. For example, there were
more than 1,000 people in the study who were not vaccinated at
all — some did not consent to vaccination, and others did not
show up for vaccination. In the researchers' analysis, they
included these people in the "delayed" vaccination group, but
it's not known whether this affected the results, Goodman said.

In addition, the researchers identified the people who developed
Ebola during the study through the regular disease surveillance
methods that are used in Guinea, but these methods might miss
some cases, particularly if the cases were less severe, Goodman
said.

Still, the researchers note that so far, they've been able to
track everyone in the study (and no one has been lost during
follow-up). This makes it likely that they've identified all the
people who have developed Ebola during the trial, Adalja said.

One person in the study developed a fever that appeared to be
related to the vaccine itself. It will be important to conduct
more research on the side effects of the vaccine, so that doctors
and patients can learn how common these side effects are, Adalja
said.